06.动态SQL和foreach

动态sql:

映射文件代码:

 1  <!-- 动态sql,根据名字和年龄查询,where标签会处理第一个and，其他位置的and不会自动处理 -->
 2   <select id="queryStudentByNameAndAge" parameterType="student" resultMap="student1">
 3     select * from student 
 4     <!-- 1.使用where 1=1 ，避免where后直接跟and -->
 5      <!-- 2.使用where关键字，避免where后直接跟and -->
 6     <where>
 7         <if test="sname != null and sname != '' ">
 8             and sname = #{sname}
 9         </if>
10         <if test="age != null and age != '' ">
11             and age = #{age}
12         </if>
13     </where>
14   </select>

foreach循环属性集合:

映射文件:

  <!-- foreach循环属性集合--><select id="queryStudentsByHomeAddress" parameterType="Home" resultMap="student1">select * from student <where><if test="homeAddress != null and homeAddress != '' "><!-- colleaction是属性中的集合，item是遍历出来的每个元素，open是循环结果前边的东西，close是循环结果后边要加的东西，separator是循环结果用什么符号分隔 --><foreach collection="homeAddress" item="homeAr" open=" and homeaddress in (" close=" )" separator=",">#{homeAr}            </foreach></if>    </where></select>

测试类:

1  Home home = new Home();
2  List<String> homeAddress = new ArrayList<String>();
3  homeAddress.add("北京");
4  homeAddress.add("南京");
5  home.setHomeAddress(homeAddress);
6  List<Student> stu = studentMapper.queryStudentsByHomeAddress(home);

foreach循环集合:

映射文件:（需要注意的是循环要循环list）

 1  <!-- foreach循环集合-->
 2   <select id="queryStudentsWithList" parameterType="list" resultMap="student1">
 3     select * from student 
 4     <where>
 5     <!-- 必须写list -->
 6     <if test="list != null and list != '' ">
 7         <foreach collection="list" item="homeAr" open=" and homeaddress in (" close=" )" separator=",">
 8             #{homeAr}            
 9         </foreach>
10     </if>    
11     </where>
12   </select>

测试类:

1 List<String> list = new ArrayList<String>();
2 list.add("北京");
3 list.add("南京");
4 List<Student> stu = studentMapper.queryStudentsWithList(list);

foreach循环数组:

映射文件:(注意循环必须都写array，输入参数不是简单类型时都写Object[])

 1  <!-- foreach循环数组-->
 2   <select id="queryStudentsWithArray" parameterType="Object[]" resultMap="student1">
 3     select * from student 
 4     <where>
 5     <!-- 必须写array -->
 6     <if test="array != null and array != '' ">
 7         <foreach collection="array" item="homeAr" open=" and homeaddress in (" close=" )" separator=",">
 8             #{homeAr}            
 9         </foreach>
10     </if>    
11     </where>
12   </select>

测试类:

1 String[] str = {"北京","南京"};
2 List<Student> stu = studentMapper.queryStudentsWithArray(str);

foreach循环对象数组:

映射文件:(需要注意的是这时的item要写循环出来的对象了，不能瞎写名字了,然后通过对象点的方式获取值)

 1 <!-- foreach循环对象数组-->
 2   <select id="queryStudentsWithObjectArray" parameterType="Object[]" resultMap="student1">
 3     select * from student 
 4     <where>
 5     <!-- 必须写array -->
 6     <if test="array != null and array != '' ">
 7      <!-- item里边写的是循环出来的对象 -->
 8         <foreach collection="array" item="address" open=" and homeaddress in (" close=" )" separator=",">
 9             <!-- 对象点属性获取值 -->
10             #{address.homeAddress}            
11         </foreach>
12     </if>    
13     </where>
14   </select>

测试类:

1 Address addr1 = new Address();
2 addr1.setHomeAddress("北京");
3 Address addr2 = new Address();
4 addr2.setHomeAddress("南京");
5 Address[] address = {addr1,addr2};
6 List<Student> s = studentMapper.queryStudentsWithObjectArray(address);